KOSSMANN, E. P. van Hees, Bibliografie van P. Geyl. BMGN - Low Countries Historical Review, [S. l.], v. 88, n. 3, p. 472–473, 1973. DOI: 10.18352/bmgn-lchr.1780. Disponível em: https://bmgn-lchr.nl/article/view/URN%3ANBN%3ANL%3AUI%3A10-1-101936. Acesso em: 30 jan. 2023.